The present invention relates to a cathode ray tube (CRT), and more particularly, to a CRT that can effectively enhance electron beam deflection efficiency.
Generally, CRTs include a panel having an inner phosphor screen, a funnel having a cone portion, and a neck having an electron gun therein, that are sequentially connected to each other. A deflection yoke is mounted around the cone portion of the funnel to form horizontal and vertical magnetic fields there. In this structure, electron beams emitted from the electron gun are deflected through the horizontal and vertical magnetic fields from the deflection yoke, and land on the phosphor screen.
Recently, CRTs have been employed for use in highly sophisticated electronic devices such as high definition television (HDTV) and OA equipment.
On the one hand, in these applications, the power consumption of the CRT should be reduced to obtain good energy efficiency. Additionally, the magnetic field leakage due to power consumption should be reduced to protect the user. In order to meet these requirements, the power consumption of the deflection yoke, which is the major source of power consumption, should be reduced in a suitable manner.
On the other hand, in order to realize a high brightness and resolution of display images on the screen, the deflection power of the deflection yoke should increase. Specifically, a higher anode voltage is needed for enhancing the brightness of the screen and, correspondingly, a higher deflection voltage is needed for deflecting the electron beams accelerated by the increased anode voltage. Furthermore, higher deflection frequency is needed for enhancing the resolution of the screen, along with the need for increased deflection power. In addition, in order to realize relatively flat CRTs for more convenient use, wide-angle deflection should be performed with respect to the electron beams. Wide-angle deflection also requires increased deflection power.
In this situation, there are needs for developing techniques for allowing the CRTs to retain good deflection efficiency while constantly maintaining or reducing the deflection power.
Conventionally, a technique of increasing the deflection efficiency positions the deflection yoke to be more adjacent to the electron beam paths. The positioning of the deflection yoke is achieved by reducing a diameter of the neck and an outer diameter of the funnel adjacent to the neck. However, in such a structure, the electron beams to be applied to the screen corner portions are liable to bombard the inner wall of the funnel adjacent to the neck (This phenomenon is usually called the xe2x80x9cbeam shadow neckxe2x80x9d phenomenon or briefly the xe2x80x9cBSNxe2x80x9d phenomenon). Consequently, the phosphors coated on the corresponding screen corner portions are not excited and it becomes difficult to obtain good quality screen images.
In order to solve such problems, it has been proposed that the cone portion of the funnel, around which the deflection yoke is mounted, be formed with a shape where a circle gradually changes into a rectangle from a neck-side of the funnel to a panel-side. This shape corresponds to the deflection route of the electron beams. In this structure, the size of the cone portion is minimized so that the deflection yoke can be positioned to be more adjacent to the electron beam paths.
However, in the above technique, the cone portion of the funnel is merely designed to be formed with a rectangular shape without considering the practical moving routes of the electron beams in various directions, and thus does not cope with the beam shadow neck (BSN) phenomenon in an appropriate manner.
It is an object of the present invention to provide a CRT that can effectively enhance electron beam deflection efficiency with appropriate structural components.
This and other objects may be achieved by a CRT with a central tube axis Z. The CRT includes a panel with an effective area and a rear portion. The panel has a substantially rectangular effective screen portion with two long sides in a horizontal axis direction, two short sides in a vertical axis direction and four edges in a diagonal axis direction. A funnel is connected to the rear portion of the panel. The funnel sequentially has a body with a large-sized end and a small-sized end, and a cone portion with a large-sized end and-a small-sized end. The large-sized end of the body is sealed to the rear portion of the panel. The small-sized end of the body meets the large-sized- end of the cone portion at a point. The meeting point of the body and the cone portion becomes an inflection point of the funnel. The cone portion has a thickness Th in the horizontal axis direction, a thickness Tv in the vertical axis direction and a thickness Td in the diagonal axis direction. A neck is sealed to the small-sized end of the cone portion. An electron gun is fitted within the neck to produce electron beams. A deflection yoke is mounted around the cone portion of the funnel. The horizontal thickness Th, the vertical thickness Tv and the diagonal thickness Td of the cone portion of the funnel in the tube axis Z direction satisfy the following condition: Th(z)=Tv(z) greater than Td(z).